There's more than one way to build a beak

Darwin's Galapagos finch beaks are commonly thought of as a
prime proof of Darwinian evolution, although in reality they only
demonstrate variety among finches. Proving that no new genetic
information was required to achieve such diverse dietary
adaptability, a 2010 study confirmed that Darwin's finches
developed 14 different sorts of beaks using the same developmental
pathways and genetic products. Control of size and curvature during
development produces the variations. Now a study of three species
of Caribbean bullfinches has uncovered surprising diversity even in
the ways beak diversity is achieved.

Caribbean bullfinches crush incredibly hard seeds "that no one
else can touch," says principal investigator Arhat Abzhanov. "You'd
actually need a pair of pliers to crack these seeds yourself; it
takes 300 to 400 Newtons [67 to 90 pounds] of force, so that's a
really nice niche if you can do that. But the question is, what
developmental changes must have occurred to produce a specialized
beak like that?" While "all modern birds share the same overall
beak skeletal structure," the three-dimensional structure of
bird beaks varies greatly. Beaks suited to a wide range of dietary
options appear in nature, equipping birds to fill many ecological
niches.

"Variation in beak shape has profound impacts on the ability of
an organism to survive and reproduce in the wild," Abzhanov and
colleagues write. "Therefore, its adaptive significance coupled to
the extreme levels of diversity observed in nature make this trait
ideal for tackling developmental and evolutionary questions about
morphological diversification in general."

"Most people assume that there's this flow of information from
genes for development to an inevitable morphology," Abzhanov says.
"Those beaks are very highly adaptive in their shapes and sizes,
and extremely important for these birds. In Darwin's finches, even
one millimeter of difference in proportion or size can mean life or
death during difficult times. But can we look at it from a
bioengineering perspective and say that in order to generate the
exact same morphological shape, you actually require the same
developmental process to build it? Our latest research suggests
not."

Abzhanov found that the same developmental
path applying the same genetic information can
produce different sorts of beaks. But he also
found that the same beak shape can be achieved
using different developmental pathways and
different genetic instructions. Thus, the
researchers report, "Different developmental programs can generate
identical shapes, and similar developmental programs can pattern
different shapes."

By geometrically analyzing the beaks of the three living
Loxigilla bullfinch species, the researchers were
able to confirm their beaks of varying size were identical in
shape. To study beak embryology, they went to the Dominican
Republic, Barbados, and Puerto Rico to collect tiny, fragile,
freshly laid eggs from dome-shaped nests often found atop tall
cacti. Beaks begin to develop around day 6 or 7.

The small bullfinch's (Loxigilla noctis) embryo starts
with a cartilage template and, under the influence of the same
sequence of control genes seen in Darwin's finches, builds a bony
beak. Its beak does not resemble any of the 14 Darwinian finch
beaks. But the two larger Loxigilla species
form bony beaks without a cartilage template under the direction of
a different combination of genes.

"Despite the fact that these birds are using different systems,
they end up with the same shape beak, and a different shape beak
from Darwin's finches," Abzhanov emphasizes, even though the system
operating in L.noctis is the same system as that
in Darwin's finches. "So that reveals a surprising amount of
flexibility in both the shapes and the molecular interactions that
support them. . . . For evolution, the main thing that matters for
selection is what the beak actually looks like at the end, or
specifically what it can do. The multiple ways to build that beak
can be continually changing, provided they deliver the same
results."

This study has not provided an example of Darwinian evolution.
It has not revealed acquisition of a blueprint for evolutionary
progress toward a non-bird. On the contrary, it hints at the
multiplicity of ways that existing genetic information can be used
to achieve diverse results. God created "every winged bird
according to its kind" in order to "let birds multiply on the
earth" (Genesis 1:21-22). This study suggests one
of the ways God equipped them to vary within their kinds in order
to adapt to changing variable ecological conditions in the
world.

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